Parallel computing applications can use multiple processes that interact with one another to produce an application output. For processes to cooperate, the processes can communicate with each other using messages that exchange data and other inter-process information.
Parallel computing applications that have multiple processes executing at the same time can also be complex and difficult to debug. For example, certain race conditions between processes on various compute nodes can create non-deterministic states. In fact, two successive runs of a parallel application with the same input may result in different process behavior.
Data dependencies are also an important area of analysis when debugging parallel processes. A group of processes may execute more slowly than desired due to a long chain of dependent calculations (i.e., a critical path), since calculations that depend upon prior calculations in the chain will wait to be executed in order. Detecting such data dependencies can be difficult when debugging parallel computing applications.
Another example of a difficult area to debug for a parallel computing application can deadlock conditions. Deadlock may exist between processes where a first process is waiting for information from a second process before the first process can proceed and the second process is also waiting for information from the first process before the second process can proceed. A more complex case of deadlock can involve multiple processes and can be hard to detect.